1. Field of the Invention
The present invention relates to a three-dimensional machining method for machining a workpiece three-dimensionally with a machine tool such as a milling cutter, and more particularly to a processing control for defining a surface to be machined and generating paths of a cutting tool to machine the surface.
2. Description of Related Art
Recently, computerized three-dimensional machining of a metal workpiece has been developed for practical use. The three-dimensional machining is generally performed based on either paths of the working end of a ball tip of a cutting tool or paths of the center of the ball tip of the cutting tool.
In either method, conventionally, a plurality of surfaces to be machined are defined individually. Every surface has peculiar outline curves and should be defined so as to reflect the characteristics of the outline curves.
Conventionally, continuous surfaces are machined separately or by transfer cutting. For example, as shown in FIGS. 8a and 8b, three continuous surfaces #i, #j and #k are defined individually (in individual coordinate systems (u, v)). In machining the surfaces #i, #j and #k by transfer cutting, the surfaces #i, #j and #k are machined continuously by transferring a cutting tool from a path to machine the surface #i to a path to machine the surface #k and then to a path to machine the surface #j. In the transfer cutting, generation of tool paths is sometimes performed based on a direction .gamma. which does not reflect the characteristics of all the surfaces. In this case, the transfer cutting is not in accordance with the characteristics of the surfaces, and the cutting may be rough or may be unnecessarily minute and wasteful. Further, for transfer cutting, a large volume of processing to avoid interference of the cutting tool is necessary, which takes a lot of time. In machining the continuous surfaces #i, #j and #k separately, on the other hand, movement of the cutting tool is generally wasteful.
Further, in generating tool paths, interference of the cutting tool with any surface must be checked all the time, which requires a complicate procedure.